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Making a glass knife (Read 28360 times)
Kjev
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Making a glass knife
Dec 26th, 2008 at 1:07am
 
I recently read a book called "Mistborn," where the main magic-using characters also carried knives made of glass for backup.

What is the best way to cut the glass? I have the pattern marked on a piece, and I really don't want to have to go to a glass shop or window repair place and A) pay for it, and B) explain what I'm doing.

Once I get the basic shape cut, I think I can do the grinding with sanding disks on my disk grinder. On the other hoof, this is an experiment, so any advice would be appreciated.

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timann
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Re: Making a glass knife
Reply #1 - Dec 26th, 2008 at 4:52am
 
Hey, I have read that book too, I now wait for book#3 in the series.
For cutting glass,  a simple "glass cutter"( Wink)  from the hardware store is the correct tool.  Should not be too expensive.
A link here recently lead me to a nice green glass "flint knapped" spear point made in Australia.  A  knapped glass dagger would be an superb cutting tool, better than grinded glass, but do not forget safety goggles Smiley
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Re: Making a glass knife
Reply #2 - Dec 26th, 2008 at 4:55am
 
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StaffSlinger
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Re: Making a glass knife
Reply #3 - Dec 26th, 2008 at 5:27pm
 
First off, you're going to want really thick glass - on the order of 1/2" or 12mm.  And a broad blade - 2" to 3" wide at the hilt on an 8" long blade.  Anything less is going to be really fragile.  Look around for someone who can do the flint knapping before you go buy glass - he/she may have done glass and know what is the best kind to use; and where to get it.
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Re: Making a glass knife
Reply #4 - Dec 26th, 2008 at 7:23pm
 
what about glass block
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Kjev
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Re: Making a glass knife
Reply #5 - Dec 26th, 2008 at 8:26pm
 
Thanks for the heads up on the glass cutter. I'll check into it when I'm in town tomorrow.

Ought to get Book 2, since I haven't read it either.

I thought about knapping the glass. My dad knaps arrowheads from glass, then colors them with an indelible marker. They are hard to tell from actual stone ones without really looking at them. He told me you generally start with a piece 5 times the size you want to end up with.

I've never tried knapping, so I opted for grinding. The glass is actually 3 layers of window glass that blew out of my shop last winter. I glued them together with super glue. Will it hold? I have no idea. This is an experiment. If it works, it goes to a friend as a display piece. When I get good at it, then I'll do my own.

Thanks for the link, too. Definetely worth reading. Smiley

As for PPE ('Personal Protection Equipment' they call it at work), I'm bringing home some safety goggles, leather gloves, and my respirator. I don't know if the respirator is actually required, but the idea of breathing ground glass doesn't sound that appealing.

The pattern I actually got from the 'Hawk Recon' knife made by Tops Knives.

(dodgy hotlink image removed)CA
I had a chance to hold one a few years ago, and I loved the way it felt.

My pattern looks like the one below.

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« Last Edit: Dec 28th, 2008 at 11:11am by Curious Aardvark »  


K'Jev  Cool
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Re: Making a glass knife
Reply #6 - Dec 28th, 2008 at 11:12am
 
well if you can get it - then hardened safety glass is what you want.
And yeah grinding glass certainly requires a mask of some kind. No you REALLY don't want to be breathing in glass 'dust'. Think asbestos with sharper edges.
 
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Re: Making a glass knife
Reply #7 - Dec 28th, 2008 at 11:24am
 
And of course you ave to realize that a glass knife has a lot of limitations. It may be really sharp, but its also really brittle. It can only be used for cutting, no stabbing. It cant be twisted or torqed. It can't be dropped or rough handled. Even tempered glass is like this. It can just take more abuse before it shatters
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Kjev
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Re: Making a glass knife
Reply #8 - Dec 28th, 2008 at 5:41pm
 
As I said, this is an experiment, and will probably just go in the guy's collection. For my own, I prefer steel.

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kuggur slingdog
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Re: Making a glass knife
Reply #9 - Dec 30th, 2008 at 11:18am
 
This guy that wrote this  http://www.sparrowcreek.com/Links_wrknapp_percusion.htm website uses the bottoms of bottles to practice knapping...
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Kjev
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Glass Cutter Woes
Reply #10 - Dec 31st, 2008 at 12:27am
 
Okay, so I bought a Kobalt brand glass cutter at Lowe's (hardware/DIY store here in the US). According to the directions, you draw a line and wa-la, the glass breaks along that line.

I tried to scribe a line. I tried to scribe it several times. This oddball thing refuses to make more than a scratch in the glass. As for the glass breaking along the line . . . yeah. Fortunately it didn't break across the pattern.

So now that I have one of these gizmos, how do you get it to actually cut the glass? It's got 6 tiny wheels in a hexagonal arrangement on the bottom, but for the life of me, I can't figure out if it's working or how to make it work at all.

Any suggestions?

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slingbadger
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Re: Making a glass knife
Reply #11 - Dec 31st, 2008 at 5:55am
 
OK, The cutter will only make a good scratch on the glass. It won't cut all the way through like some people think. So. What you want to do is use the cutter to scribe out the pattern. You may want to go over it a couple of times, just to make sure the scribing is consistent. Wear gloves for the next part. Put the scribed line on the edge of a table,with the waste part hanging over.With one hand, hold the piece on the table. With the other,apply gentle downward pressure on the waste part and it should break cleanly along the scribed lines. This will probably take some practice. Small pliers can also be used for taking off small bits of the glass.
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The greatest of all the accomplishments of 20th cent. science has been the discovery of human ignorance  The main difference between genius and stupidity is that genius has it's limits.-Einstein   I'm getting psychic as I get older. Or is that psychotic?
 
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Re: Making a glass knife
Reply #12 - Dec 31st, 2008 at 7:06am
 
Sorry I got to this discussion late, I could have saved you some pain.
KNAPPING is what you want to do. A knapped glass knife has a superior edge but it takes a long learning curve to master knapping glass. You will want to buy a couple boxes of band aids before you start.
A glass cutter for a glass knife?  Not so much. Well, maybe to get the basic blank cut from stock.

Historical glass knives were small and single edged,  A dagger? I've seen the real thing, about 5" long.
Fictional glass daggers were longer, but the fictional characters that used them were more skillful then we are.

Resources:
GLASS SHOP SCRAPS: Large pieces of plate glass like store front or tempered glass for table tops.  You want it up to about a 1/4" thick.
CERAMIC SHOPs: Mold the size blank you want from slurry. Ceramic is glass but the grain pattern is consistent.
ON LINE: look for obsidian suppliers. Obsidian is black volcanic glass and is the prize for knapper made knives. For instance: http://www.stoneknapping.com/knappingmlb01.html

My experiance:
I have been knapping flint, glass and obsidian for a while. I can make a servicable knife and arrow point.
My one obsidian knife has a two inch blade and is simply a rock with an edge you could almost shave with if it were'nt for the serrations.
But, who wants to shave when they go primitive?

Good topic. Good luck
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ChuckRocks
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Re: Making a glass knife
Reply #13 - Dec 31st, 2008 at 7:20am
 
Forgot to add:
Glass cutting needs only the smallest cut to break the surface. You don't need to see it for it to be there.
A heavy score leaves side fractures in the cut and can allow the cut to wander.

Rules:
Start with scraps for practice.
Make sure the cutting disk is clean and spins freely.
Clean the glass.
Lube glass with light oil.
Use a straight-edge guide.
Produce a fine scratch without a lot of pressure.
Break glass by bending it over an edge with the cut side out. (Wear gloves for this part.)

Look it up on-line to be sure you're doing it right.

Good luck.
Post photos.

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kuggur slingdog
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Re: Making a glass knife
Reply #14 - Dec 31st, 2008 at 8:40am
 
Hmmm, I know where to find big chunks of obsidian....
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